I have only given this a four star rating purely because I have only had one other product to compare it by and even that didn’t put up much of a fight.
People taking the time to fill these reviews is how I came to buy the Discovery 640.
Doing a spot of research pays of when buying something you have no previous experience of. The blue tooth head set I received with my phone was awful, very poor sound quality and more often than not I ended up removing the hands free ear piece and using the phone directly, not a good idea if you don’t want to receive a ticking of and fine from the local police for driving while using the mobile.
I found the Discovery to be everything I had read in a number of reviews, extremely light and with superb sound quality. I would not say I forgot it was in my ear at any time but it was not obtrusive at all, wearing it for long periods was also not a problem.
I am still trying out the three different size ear pieces to find the one which fits best as so far the only problem I have experienced is it falling out of my ear on occasions. Discovery does come with an extensive kit for power adaptors and charging accessories and there is even an adaptor for charging from a battery, Plantronics have really put some thought into this product.

Once paired with the phone the Discovery is very easy to use, answering and terminating calls from the earpiece itself. Stand by and talk time are also very good.
At the end of the day all you want from a hands free kit is to be able to easily hold a conversation and not struggle to hear or make yourself be heard and the Discovery excels at that. What more can I say.
So far I’m extremely happy and would easily recommend it to anyone

IMO the Discovery 640 headset is one of the coolest looking among the current crop. It’s compact and lightweight, plus it’s really comfortable on the ears with it’s innovative in-ear gel. Installation and configuration is a breeze, I was already making my first call within minutes. I’m glad I ditched my stock Nokia headphones for this one.

Good headset which is very easy toset up. Using on a RAZR V3. Very light. Good sound, mainly used in the car

Only down side is the holder does not clip well onto shirt pockets

I’ve been pleased with this Plantronics Discovery 640 Bluetooth Headset as it addresses some of the deficiencies I found with other headsets.

The headset fits snugly into my ear without the optional ear hook.

When not in use, the headset is stowed in a protective case with pen clip. This case also acts as a charging station and can be used with your existing mobile phone charger by using one of the supplied adaptors. This cuts down the amount of equipment you carry. There is also an emergency charger that charges the headset from an AAA alkaline battery. I haven’t used this but it seems a nice touch.

All these bits are organised in an aluminium storage box, rather than lost in your pocket or bag!

Overall I think the product has been thoughtfully designed.

I have noticed that my headset did not fit securely in its protective case causing an intermittent connection during charging. Plantronics support say they have had problems and improved the design. They are sending me a new case.

In my experience it is best to wear the headset on the same side of your body as you carry your phone as reception, though it still works, deteriorates though your body mass! This may be due to the small size of the headset and its even smaller internal aerial.

Bluetooth is Bluetooth is Bluetooth! No it isn't!
Having tried a few types of headset, the Plantronics 640 is different.
A really lightweight, compact unit which is excellence itself, setup is simple to virtually any comatible mobile tried. Range is good approximately 20 feet away from 'phone before breakdown of signal. Speech clarity near perfect with one test sounding like the preverbial 'Head in Bucket' but then it was in a fully tiled room. Good noise cancelling features on the move, as a pedestrian in a busy and noisy thoroughfare very little ambient sound was picked up and vehicle mobile use was excellent with no ambience whatsoever.
Charging options are absolutey first class with adaptors that cover most situations therefore eliminating the annoying drop-out through lack of battery power. Of course the case is a must for storage of the various components but again well made, compact and a must have addition, especially to suppliers that sell the 640 without it and at additional cost.
My only critisicm would be the vehicle stereo becomes very mono owing to the near perfect fit of the gell ear inserts but then I consider that a minor issue.
Overall impression damn good value for money from Ligo.

I have used my fair share of bluetooth headsets (including Sony Ericsson, Omiz, Motorola, and Jabra) with a fair share of phones, including ones with AND without bluetooth.

The attraction to buy this headset was that it was the first (and only) one in the market to be able to bind 2 headsets at the same time. I have 2 phones, 1 personal and 1 work, so driving can be annoying, as i have to set 1 phone to forward to another, then bind the 2nd phone to the bluetooth headset. With the 640 being able to bind both at the same time, there was no hassle. Also, this headset uses V1.2 bluetooth, which has better connectivity specs (connection and disconnection channels) - compatible with V1.1 and V1.2 bluetooth phones.

Also, with the experience of using different headsets, the 640 seemed to be the quickest one to connect to the speech path, compared to previous ones i've used. Some headsets, once you press the button to answer, it can take up to 3 secs for the speech path to be connected, although the call is already answered.

The holder can also vibrate when the headset is held in it. If there is an incoming call, the holder will vibrate, and once you pick up the headset, the call is answered, so no more button pressing and confusion.

Battery life is great - had it for 3 days in a row over the weekend and it was fine.

However, there are 3 downsides to the headset - mainly design issues - hence the 4 stars

1) the holder doesn't really 'hold' the headset tightly enough (is very loose) so it may fall out easily and the vibrating holder does not work if the headset is correctly fitted to the holder.
2) the design of the 640 is very male-orientated - only the 'clip' is available, no other options of holder the headset in the holder.
3) I have a K608 and have had trouble using the sony ericsson charger to charge the headset (with the correct adaptor). I have known it to work with some sony chargers, but apparantly not all types (according to plantronics tech support). However, Nokia works, and so should Motorola - I don't have access to a siemens charger.

I am a choosey and demanding technology user, but this headset is the best piece of communications kit I have ever bought. It is simple to configure, easy to use, incredibly reliable and weighs next to nothing. It fits lightly inside your ear without being intrusive, and is perfect if you are a spectacle wearer ( I use it without the ear loop and it never moves or becomes dislodged). Buy it!

I have used Sony Ericsson Bluetooth headsets in the past (including the very first Bluetooth headset to market), and so this was quite a departure from my normal choice. I have to say that I don't regret making the move away from my usual brand having had the Plantronics device for a week now.
I was pleasantly surprised how well the in-ear gel holds the headset in place - this was one of my primary concerns when considering the purchase.
Sound quality is very good, with excellent volume range for the wearer and apparently very clear audio for the other party. I did find that with many of the Sony Ericsson headsets that the other party would complain that the volume of my voice was a bit low.
Bluetooth range is nothing special, and I have come across other headsets that perform a bit better in that respect, but it is nonetheless perfectly adequate for wearing the headset on one side of the body with the phone in a pocket on the other side of the body.
Last number redial is a feature that I've not had on previous headsets, and I have to say that it's very useful when you are trying to get hold of someone who is unavailable - the phone can stay in your pocket.
The whole kit seems nicely designed and thought out, with the possible exception of the ear gel being exposed when the unit is carried, unless it is carried in the unpocketable presentation case. The problem is that the ear gel collects dust etc. if carried in a pocket and does not do quite as good a job at securing the headset in the ear after a while. I may have to invest in some spare ear gels.
Despite this I would have to rate the headset very well as a whole. It is highly portable in terms of size & weight, with great sound.

Amazingly light and very comfortable - I forget that I'm wearing it.
Takes a bit of time to get used to how to actually work it - I kept either turning it off or not ending my call at first, but ok now.
Other occupants of my car complain about the blue indicator light flashing every 6 seconds, but I dont see it